I would have thought that it shouldn't have been possible for a podcast to be owned by two separate IDs.
So, you contacted them at https://podcastsconnect.apple.com/contactus, they asked you to add something to the feed and you did that, and you told them the new ID - correct?
Can your friend sign in at https://podcastsconnect.apple.com and select the podcast, and then be able to see all the details and administer it?
What happens if you sign in there - can you select the podcast and see the details?
These instructions might also help:
It is possible to transfer the ownership of a podcast to another Apple ID: poster tcarreira did this and has posted the method:
0 - Contact apple support from the current owner of the podcast: Contact Us -> Podcasts(My Issue Is Not Listed)*.
... wait for them to answer with further instructions and a code...
1. Insert the authorization code “xxxxxx” in the <itunes:keywords> or <copyright> tag.
2. Verify that your Apple ID is activated.
3. Obtain the direct link to your show on Apple Podcasts.**
4. Customize the statement below, and paste it in your reply to this message.
I authorize changing management in Podcasts Connect and access to Podcast Analytics to the account [Apple ID email address]. As requested, I have inserted the authorization code in the [specify tag] tag.
Paste the direct link to your show on Apple Podcasts
*Go to Apple Podcasts for Creators and click the 'Contact Us' link at the bottom of the page.
**To obtain the link in Apple Podcasts app (Mac - Catalina) find your podcast and click the three dots icon to the right of the 'Subscribe' button and choose 'Copy Link'. In iTunes - control-click (Mac) or right-click (PC) on the podcast image (or where it should be) and choose 'Copy Link'.
I'm not sure the Support email address you were given is valid any more. Try:
https://itunespartner.apple.com/contact/?content_type=podcasts
Occasionally people have been unable to get through to that contact page. If so, contact Support. Don't report it as a podcasting problem - they don't handle those - but as an inability to get to the contact page.